Title : Design, Synthesis and Study of Catalysts for Organophosphate Ester Hydrolysis.

Descriptive Note : Annual rept. 15 Mar 83-14 Mar 84,

Corporate Author : ALBERTA UNIV EDMONTON DEPT OF CHEMISTRY

Personal Author(s) : Brown, R. S.

Report Date : MAY 1984

Pagination or Media Count : 42

Abstract : We have prepared several tris-imidazol-2-yl phosphines (9-12) and evaluated their Co(2+) and Zn(2+) complexes as catalysts for the hydrolysis of p-nitrophenyl-picolinate (13) and ethyl-p-nitrophenyl methyl phosphonate (14). For the hydrolysis of 13, the Co(2+) complexes of bis(4,5-diisoproylimidazol-2-yl)-imidazol-2-yl phosphine (12) appear to act by a common mechanism. Plots of K sub obs (the observed pseudo-first order rate constant for the hydrolysis of 13 catalysed by 11:Co(co(2+) or 12:Co(2+) as a function of pH show two regions, suggestive of formation of an active L:Co(2+)-OH-unit. The pKa's of the L:Co(2+)-OH2 speciesw of both 11 and 12 are also found to be 7.6-7.8. Kinetic analysis reveals that the basic forms of the complexes are acting as bimolecular nucleophiles toward 13. Hydrolysis of the phosphonate ester 14 is promoted by 12:Co(2+), the reaction rate increasing in a first order way with (OH(-)) from pH 7.4-8.3. Since there is no signoidal titration behavior of the rate at pH (7.6-7.8 suggestive of active 12:Co(2+)-OH(-) form, the mechanism of hydrolysis of 14 by 12:Co(2+) must be different from that found for the hydrolysis of 13. Complex 12:Co(2+) is at least 5-fold more active than is 11:Co(2+), although the latter precipitates from the reaction mixtures, which makes comparison difficult.